Measurements of alpha-LA and casein levels, their messenger activities and mRNA sequences in the gland show that these differentiated functions are expressed with the onset of gestation. Biphasic expression of these proteins during the second and third weeks of gestation is measurable by their protein levels, messenger activities and mRNA sequences. The mRNA levels are, however, out of phase with protein levels during the first week of gestation, but remain in phase thereafter. The results show phasic and sequential expression of these differentiated functions during lactogenesis.